Detector system



R.VHLEM DETECTOR SYSTEM Oct. 30, 1934.

Filed A ril 21, 1951 3 Sheets-Sheet l llllllllXXIlXX imrwzxmr INVENTOR RAYMOND VIU EM "BY P ATTb NEY I R. VILLEM DETECTOR SYSTQEM Oct. 30, 1934.

Filed April 21,. 1931 3 Sheets-Sheet 2 INVENTOR RAYMOND VILLEM BY 7% g/ we/ ATTORNEY 5 Sheets-Sheet 5 R. VILLEM DETECTOR SYSTEM Filed April 21, 1951 Oct. 30', 1934.

INVENTOR RAYMOND VILLEM BY 7 v A OR EY Patented Oct. 30, 1934 UNITED STATES PATENT OFFICE DETECTOR SYSTEM Application April 21, 1931, Serial No. 531,713 In France May '6, 1930 5 Claims. (01. 250-) The present invention (system Villem) concerns a method and improved means useful in communication by radio frequency oscillations.

'In radio-electric transmission, especially on short waves, variations in intensity or signal strength are frequently observed, and these must be compensated by anti-fading devices which are brought to act upon the sensitiveness of the receiver in order that, at the output end thereof, signals of constant amplitude may be insured.

The action of the said devices is attended, however, with a reinforcement of the stray noises, and these will be so'much stronger inasmuch as at the time when the signal strength falls off the amplification of the receiver is pushed to a higher value.

It is easy to understand the trouble resulting fromsuch an amplification of the stray noises, especially in the recording of telegraphic signals or in the operation of apparatus adapted to suppress echo effects, when a radio-telephonic connection is concerned which is established with a network comprising subscribers. In both cases, as amatter of fact, it has been necessary to produce by the action of signals (telegraphic signals or voice currents) a direct current from a detector device and which is utilized for actuating 'a relay of mechanical or electrical nature or tube type, controlling the recorder or inking meansof 130; the signals (in telegraphy work) or rendering a line impermeable for the voice or speech currents (in telephony work) It will-be evident that when the noises grow at the time when the amplification of the receiver apparatus is enhanced, they are liable to assume a value suflicient to act like a signal and thus cause undesirable operation of relays. The system hereinafter to be described and which forms the object of the invention serves the purno; pose of obviating this inconvenience.

.The basic principle of the device consists in opposing, in the detector device controlling the mechanical or electrical relays, the currents coming from the receiver to currents proportional to the amplificationf actor of the receiver, said factor being made variable by the anti-fading system. The-amplitudes of the opposing currents are reg 'u'lated in away so that their dilference represents the amplitude of the currents furnished only by the signals.

The invention will be understood by the following detailed description thereof and therefrom when read in connection with the attached drawings, in which: i

Figure 1 shows a circuit arrangement which includes the gain regulation and the noise compensating features of the present invention; while,

Figures 2 and 3'show modifications of the arrangement of Figurel.

Figure 1 relates to the application of the present scheme to radio-telephony. Referring to the drawings it will be noted that various parts are enclosed in dash-line boxes. Part I represents a radio frequency amplifier of the signal connected with the .input line Is and whose amplification factor is made a functionof the carrier wave by the agency of the shunt tube 1 in unit V. For this purpose, as known in the art, the filament-plate resistance of this tube is controlled by acting upon its grid potential which in turn is a function of the current furnished from the detector II amplified by the direct current amplifier IV. "The latter is acted upon by, or comprises in its circuits, a low-pass filter F filtering the voice currents. The purpose of the filter F is to pass only the components of the voice frequencies or-of the code signals and to stop or shunt out all other alternating current components.

Part III represents the audio frequency amplifier of the signal which is fed to the subscriber by way of an end transformer of well-known type VI furnished with a line Ze balancing the subscribers line la.

Part VII represents the modulation amplifier of the transmitter which, in order to prevent echo effects (re-transmission of incoming currents when the end or output transformer is not balanced), is blocked by the incoming currents by means of the controlling detector VIII which constitutes one of the elements of the system here disclosed. In the case of the illustration referred to the blocking of the modulation line Zm is effected by acting upon the grid of an amplification stage comprising two tubes connected push-pull fashion, though it will be understood that the blocking could also be insured by the aid of a relayshort-circuiting or cutting the modulation line.

It will be seen that the grid G1 of the detector VIII is supplied simultaneously by the output currents of the receiver and the direct current produced by the anti-fading amplifier IV. As the said direct current flows through the resistance R it sets up a direct current potential being a function of the amplification of the signal in I. The grid of the detector VIII is polarized negatively from the battery P so that it has a convenient value. I

The operation of the scheme is as follows:

At a given instant, let isf represent the intensity (current) of the incoming signal, let i represent the intensity of the stray noises, and let Is and Ip represent the respective intensities after detection and suitable audio frequency amplification of the signal and the stray noises furnished to the end transformer.

When the signal fades the detector of signal II arranged, for the sake of illustration, in a way known to produce grid current detection, tends to provide at its output end a larger current is which, when flowing through resistance 2, occasions at the grid 1 of the tube in stage IV an increase in negative potential. The result is a decrease in plate current i1 which, owing to its flow through resistance r1, causes a reduction in the potential of grid g2 resulting in turn in a growth of plate current I fed to the output resistance R of the direct current amplifier of the anti-fading device. This current by virtue of its flow through the resistance R sets up at the grid G a negative potential which tends to increase the filament-plate resistance of the shunt tube and thus occasions a higher amplification of the signal whereby the loss in strength or volume of-the signal is counteracted. It follows that if the intensity of the signal has become there will be obtained an amplification K times greater in the amplifier I, and the stray noises will have a value K times larger than before and will thus be liable by themselves to cause a detected current furnished by VIII suflicient to block the amplifier VII. In order to prevent this from happening, the direct current I, produced by the antifading device IV, is used for desensibilizing the detector VIII. To insure this result the potential produced by this current in a por. tion R, suitably chosen in the resistance R, is

fed to the grid G1 of the control detector VIII so as to impart to the latter a negative potential, the value of which will increase with increase of the current I. In other words, at the time fading occurs the amplification of the signal, and consequently of the noises, will be larger.

In the case shown the amplifier IV is utilized simultaneously for the operation and the desensibilization of the control detector, although it will be understood that, without departing from the invention, it is evidently possible to use distinct amplifiers or amplifiers having parts in common.

The system is regulated as follows:

The cell or battery P is regulated so that in the absence of signals, or voice currents the grid potential of tube VIII is of such a value so that, for the lowest amplification of I, that is to say, for minimum stray noises, the plate current of the control detector VIII is of zero value or very low, and consequently there is no action upon the amplifier VII. Then, in the absence of signals, for the highest amplification of I, and with an incidental maximum of stray noises, the value of R is regulated in a way so that the current furnished by the control detector VIII is still of zero value. It will be evident that, under these conditions what is obtained in the detector VIII is a compensation of the stray noises due to the variations in amplification of I that is necessary to insure a signal of appreciably constant amplitude or volume (save for a certain regulation factor) in such a way that the blocking of the amplifier VII will take place solely under the action of the signal only.

It will be obvious that the system is equally applicable to telegraphy work. In this case the control detector actuates a relay and the circuit arrangements are as shown in Figure 2, where the same reference letters denote the same elements as in Figure 1. By way of modification and in order to illustrate the general applicability of the system detection of the signal, in Figure 2, is effected by way of plate characteristic and compensation of fading by acting through the negative grid potential upon the amplification of the signal. In what follows the assumption is made that the signal is modulated either at the sending end or at the receiving end in accordance with ways and means well known in the art.

Repeating what has been said before in the case of Figure 2, it will be readily understood that if the signal carried by the input line 25 fades, id tends to decrease (owing to plate detection), the negative potential of 91 diminishes in absolute value, i grows, and by virtue of the fall of potential across resistance R, desensibilization of the control detector VIII is insured, while the negative potential of g2 grows in absolute value. The current I falls off and its flow through the resistance R diminishes the negative grid potential of the tube L and increases its amplification of the signal.

The purpose of the filter F is to pass only the direct current components and to block or to shunt out the audio frequency alternating. current components. The purpose of this is to prevent the armature cooperating with the relay P from oscillating at each modulation beat and to permit it to respond only when the modulation ceases entirely. In telegraphy work the signal is constituted by modulating a carrier wave by a continuous wave and the duration of such modulation represents dashes or dots. It is, of course, necessary that the relay should not respond to each alteration of the modulation but should respond to these dashes or dots.

In the operating circuit of the relay P is included an audio frequency filter F so as to avoid vibrations of the keeper under the actionof lowfrequency signals.

Finally, it is also possible to operate the control detector by rectified audio frequency signals in correlation with the direct current compensating potential supplied from the anti-fading device. Figure 3 represents an embodiment of this system utilizing a control detector VIII comprising two tubes, the actions of which upon the relay P are compensated for the growth in stray noises at the instant the signal fades. It will be seen from Figure 3 that when the signal brought in by way of line ls falls off in intensity upon reception, the growth of stray noises, due to the operation of the anti-fading device, insures an increase in current furnished by the second detector IX and a decrease in the current produced in the resistance R of the limiter tube V. What results is a decrease in the absolute value of the negative potential of the grid G1 and a growth in the current I1 flowing in the winding S1 of the relay.

This growth of current, which, during a keying intermission or spacing would tend to cause operation of the relay in the manner of a signal or result in sticking between signals, looked at from the viewpoint of its effect upon the relay, is compensated by an increase in current I2 which also tends to re-establish to its proper position the keeper or blade being'pivotal about point 0. It will be readily understood, indeed, that at the instant when the signal fades the current la issuiinglfromdetector II tends to decrease resulting in algrow th of in) and a decreaseof the current I, which, while flowing through the resistance R, is, Ionthe one-hand, associated withadecrease of the :ne'galtiv'e potential of the tube L with an incidental reinforcementof the amplification of the :signal, andyon the other hand, by means of the tap of the grid of G2 established across part R of the resistance R diminishes the negative potential of G2 which thus leads to a growth of the current of I2. It may be noted that this latter modification and embodiment is serviceable in the case of modulated telegraphy (at the transmitting or at the receiving end) effected either with or without suppression of the carrier wave in the intervals between signals. (Telegraphy with suppressed carrier wave amounts to the case of an infinitely feeble carrier wave during inter-signal intervals or spaces.) As a matter of fact, it is feasible to regulate the time-constants of the filter circuits F1 and F2 to equality with a high degree of preci sion so that under normal or permanent working conditions the potentials applied to the grids G1 and G2 obey the identical time laws.

The invention is capable of a great many modifications other than those here cited by way of example which by no means are intended to limit the scope of the invention, for any particular,

application.

Improved method of receiving signals transmitted by radio frequency oscillations consisting simultaneously in automatically varying the amplification of the said oscillations for compensating their fluctuations in the volume of the incoming signal and to oppose to the detected signal current (or to the effect of this current) another current (or an effect thereof) in accordance with the variations of amplification of the oscillations with a view to compensate the undesirable action of the stray noises acting at the input end of the receiver, the value of which compared with the signal grows with an increase in amplification.

Improvement in amplifier and receiving means for radio frequency oscillations wherein the amplification is automatically adjusted in such a way as to compensate the variations in volume of the signal at the receiving end (fading). characterized by the feature that the output or useful current of the apparatus is the resultant of the differential action of or opposition between the normal detected current and a compensating current according to the variations in amplification.

The compensating current is furnished by the direct current amplifier regulating the amplification of the input amplifier or else by a distinct amplifier.

This current (or a potential derived therefrom) is subjected to a differential action either by the intermediary of relay tubes or directly by the current or potential normally furnished by the receiver to the means translating the signals before before mentioned.

Having thus described my invention and the operation thereof, what I claim is:

1. In a receiver system for radio frequency signals comprising the control of the amplification 'of radio frequency energy bythe detected current, the method of suppressing noise resulting from the increase in amplification when the signal fades, which includes the step of causing opposition between the effect of the detected current and the eifect'of a direct current varying in proportion to the radio frequency amplification.

2. In an apparatus for receiving radio frequency signals, means for amplifying said radio frequency signals, detecting means associated with the output of said amplifying means, an output circuit connected with said detecting means, said output circuit being responsive to the detected current, means for controlling the amplification of the said amplifying means, said controlling means being controlled by the detected currents in said output circuit, signal indicating means, a circuit fed by said detected current and associated with the said signal indicating means, a direct current source, means for rendering the direct current from this source proportional to the amplification characteristic of the radio frequency amplifier, and a connection between the direct current source and said circuit, said connection being traversed in opposite directions by the direct current from said source and the detected current from said output circuit.

3. Means for receiving radio frequency signals comprising, a radio frequency amplifier, a detector connected with the output circuit of said amplifier, an output circuit connected with said detector, said output circuit forming a path for the detected current, means for controlling the amplification characteristic of said amplifier, said controlling means being controlled by the detected current flowing in said output circuit, signal indicating means, a circuit connected on the one hand with said signal indicating means and. on the other hand with said output circuit, said circuit being fed by detected current from said output circuit, a direct current source associated with said amplification controlling means, means for rendering the direct current in this source proportional to the amplification characteristic of said amplifier, and a connection between the direct current source and said circuit, this connection being traversed in opposite directions by the direct current from said source and the detected current from said output circuit.

' 4. Means for receiving radio frequency signals comprising, radio frequency amplifying means, detecting means having an input circuit connected with said amplifying means and an outa put circuit in which the detected signals flow, means for controlling the amplification characteristic of said amplifying means, said controlling means being controlled by the detected current in said output circuit, signal indicating put circuit of said control means, a tap on said resistance, and a connection between said tap and said circuit whereby the effect of the direct current in the resistance is opposed to the effect of the signal detected current.

5. Receiving apparatus for radio frequency sig- 3 nals including, amplifying means, detecting means having its input circuit associated with said amplifying means, and an output circuit in which detected signal currents flow, means for controlling the amplification characteristic of proportional to the amplification characteristic of said amplifying means, and a connection between the direct current source and the rectifying circuit, said connection being traversed in opposite directions by the direct current of said source and the rectified signal current.

RAYMOND VILLEM. 

